Bridgeport Series 1 and 2 differences

[Wirecutter]

Only complaint with the VFD is it makes my VRO do the hula if the motor is running on the high speed windings.
Marc-

Obviously, this shouldn't be happening. FYI - I have a SquareD Altivar 16 rated at 2HP running a 1 or 1.5 HP motor. My DRO is a Newall C80. I've wondered (worried?) about the VFD or other machines interfering with the Newall, but so far, it hasn't been a problem. I've even used the MIG welder while the DRO was on, and everythng is fine. (That's the exception, not the rule - usually just about everything else is off when running the welder.)

FWIW, you may want to check wiring and grounding in the shop. Keep wires in and out of the VFD as short as you can, and maybe get a filter or two. IIRC, there is a filter kit available for the Altivar (and probably most other VFDs) to address these kinds of problems.

It may not be much of an issue for you, but personally, little demons like that just annoy the bejesus out of me and I'd want to track it down.

Oh, and changing the belts on the step pulley Series I is really not so hard, it's just "one more thing" and can get annoying - that's why I love the VFD so much.

It's exactly this "one more thing" annoyance that has me working on the cheap power drawbar project. I saw a posting here that mentioned it, and got the plans and parts. It'll be a cool thing to have, especially with the back and spine troubles I've had of late. (Long story.) I'll be sure to brag and post pictures of the completed results.

-Mark

[Marc M]

Obviously, this shouldn't be happening....

-Mark

Thanks for the tips. I have an Allen Bradley 1305-12 VFD driving the mill. The correct AB filter is also installed. All grounds were verified and there are no ground loops. All connections are made with liquid proof BX, properly bonded. The VRO (video read out) is an Acu-rite 300M that employs a CRT rather than conventional vacuum-fluorescent, LED, or LCD display. The magnetic field generated by the high speed windings of the motor are strong enough to interfere with the CRT. The cost of EMI shielding is more than I want to shell out. I can run the motor off the low speed windings without any problems so that's where it normally stays. I've got the VFD upper limit set to 90hz so I can regain some speed. If I'm doing something that needs higher speeds, I just switch to HI and deal with the display wobble. Incidentally, I left the drum switch wiring intact and simply removed the knob so it can't be accidentally shut off while under VFD power.

Also, just so happens I finished up my cheap power drawbar last night. I did run into a few problems though. First thing was the dimensions on the prints for the air wrench mounting weren't correct. It seems there's some variance in manufacturing so be sure to measure your wrench. The reverse valve in the wrench wouldn't seal either. Turned out there was a chunk of o-ring jammed in it. I did a few things different from the plans. I'll get some pics and post them in the next couple of days. Have Fun!

Marc-

[HTRN]

Not knowing "what you've seen" makes your experience base questionable. The fact that you've never seen a Series II Special, when there are thousands of them out there, gives me some hint that "what you've seen" isn't much.

You know what they say when you "assume"..


HTRN

[jeep534]

I've honestly never seen a "Special". And from what I've seen, the Series II's the last coupla years have consistantly garnered less money than the Series I. It might be different where you are, given the nature of the local machine shops(big work requires big machines).

As for the Pulley/Variable speed deal, I too think a pulley machine with a VFD is a better way, no sheeve problems, and the machines are generally cheaper. I'm surprised the clone mill makers haven't made this a standard option, and skipped the stack of pulleys for a coupla cogged belt pulleys(instead of 6 speeds it would have two) and a VFD..


HTRN

Well I have seen a series II special with a Jhead. that must be the "holy Grail" for the bridgeport guys. I have a wells Index 847 , A lagun CNC, Steinel Small manual, and A bridgeport R2E4(boss9) CNC. I dare say that the next mill I buy will be a Series II special with a "J"head and Bridgeport power feed. being driven with a VFD.
Just My Humble Opinion. it would even better if I could get it with a NMTB-30 spindle
Happy Hunting
archie =) =) =)

[Mark Hockett]

I'm surprised the clone mill makers haven't made this a standard option, and skipped the stack of pulleys for a coupla cogged belt pulleys(instead of 6 speeds it would have two) and a VFD..


HTRN

There are a few companies selling inverter based variable speed knee mills.

http://www.acergroup.com/em-3vs.htm

If I ever buy a new knee mill that is what I will get. I have both a step pulley and a standard vari speed in the shop now and I like features that both have. My step pulley machine reaches over 5000 RPM which is great for small end mills, but its not as easy to change speeds. The vari speed only gets to 4000 RPM but is easy to change speeds. The noise issue with the vari speed heads is sometimes caused by the plastic sleeves in the sliding pulleys wearing out. I have changed my pulleys to a newer style with bronze bushings. It is now quite except for a little belt noise sometimes.

[pcarpenter]

I have railed here on the wisdom (or lack thereof) of setting a belt to a fixed position and using a VFD for huge variability in speed. If you must do this, pick a belt setting (ratio) that approximates 1:1.

Would you hop on a ten speed bike, put it in tenth or first gear and say "I am going to use this gear for everything and just pedal faster or slower"? You can see where the loads presented by a steep differential between pulley diameters greatly affects the load seen by the motor and the rest of the drive line. There is no good reason to go overboard on the "gee I've got a VFD and so now I never need to consider the ratio between the motor and spindle" thing. Will your motor survive this? Probably. That still doesn't make it a good idea. If you say set the belt to a high speed range and then slowed the motor down using *very* low frequency power to reduce its speed, then you loose torque (at the spindle) as compared to setting the belt to roughly direct drive and reducing line frequency less.

I've got a well used VS head model and have replaced the plastic bushings in my VS. head and had the entire head apart and went all through it. The VS portion of the drive is actually very simple and certainly not that prone to wear by us home shop types. It's probably like everything else...its a big deal until you have actually done it. It may have been less of an issue for me since I was going to tear it all apart anyway. It's continuously variable and did not cost me an extra $300 like a VFD, although I do have to grumble a bit over the $70 or so it costs for a VS belt.

[Marc M]

... wisdom (or lack thereof) of setting a belt to a fixed position and using a VFD for huge variability in speed. If you must do this, pick a belt setting (ratio) that approximates 1:1....

I agree that to become married to a single belt position/motor speed combo is short sighted. Most guys recommend you eliminate the drum switch and wire directly to the high speed motor windings when using a VFD to prevent accidentally switching the motor off and Chernobyling the drive. I didn't want to loose that flexibility either. I think a much better solution is to simply remove the knob from the drum switch so it can't be accidentally used. If that's not possible I'd put a cover over it before I'd loose the ability to switch motor speeds. If I had idiots working around the machine I'd wire the cover to the 'enable' input of the VFD to shut it down if the cover was opened. My approach is to think of the motor/pulley/backgear combination as the coarse speed setting, and the VFD for the fine adjustment. With BP type machines, changing belt positions is so quick and easy so I can't imagine why anybody would stick to a single position.

[Wirecutter]

Would you hop on a ten speed bike, put it in tenth or first gear and say "I am going to use this gear for everything and just pedal faster or slower"?

Actually, I have real live experience with this, only I put it in top gear. I was 17 and in love, and this was the ride I used to get to and from my girlfriend's house 2 miles away. I could race someone with a regular 10 speed and beat them because I didn't have to switch gears. The bike suffered a lot though. I broke one or two steering goosenecks, and wore out the cranks and bottom bracket stuff pretty badly. Fancy alloy steel and aluminum are no match for youth and raging hormones.

My approach is to think of the motor/pulley/backgear combination as the coarse speed setting, and the VFD for the fine adjustment.

This is pretty much what I said, too. I can set the output frequency of the VFD to something below 10Hz and still have the mill run, but that doesn't mean I think it's wise to do so. I'm no motor engineer, but that seems like it would be a bit hard on the motor.

When I first got the mill, I was faced with the problem of finding 3-phase power for it. The VFD was cheaper than a rotary, and didn't threaten the abuse of the motor that a static converter did. Getting all the fancy speed, acceleration, and deceleration control was just a bonus. Not bad for $100 off of ebay.

-Mark

[Swarf&Sparks]

Something I haven't seen mentioned on various speed control threads. If you slow a motor under load, current is proportional, likewise heating. There is a fan attached to said motor shaft, slowing, so less cooling. Draw your own conclusion.

[John Williams]

HTRN, the link in your sig is bad....should be

http://thisoldshed.tripod.com/

Looks like the start of a good personal shop page, once you get some more projects....

John

[Milacron of PM]

Something I haven't seen mentioned on various speed control threads. If you slow a motor under load, current is proportional, likewise heating. There is a fan attached to said motor shaft, slowing, so less cooling. Draw your own conclusion.

True. The solution is a seperate fan motor. I once imported leadscrew a tapping machine from Italy where they did just that.....a seperate small motor sat on top of the spindle motor, driving the fan rather than the spindle motor shaft driving the fan.

[dicks42000]

Belt swapping....

OK, while I don't own a Bridgeport, I have a Rockwell vertical now, and used to have an Elliott Milmore....
Being a short guy, I'd say I'll go for a VFD on my Rockwell when I get around to it. I use a milk crate to stand on to swap speeds on the Rockie. It gets kinda old....Also belt life in low speed suffers due to the tight radius of the pulley. I did make moving the motor easier by using some thrust washers between the motor & the head casting...

[JPR]

In keeping with Mark's idea of some type of safety on the drum switch, you could add the very slick safety that Frank Ford shows on his website.